This invention relates to lift type, vertical axis windmills. More specifically, the present invention is directed to a lift type, vertical axis windmill having an omnidirectional diffuser. A friction heater is also included.
Vertical axis windmills employing aerodynamic lift rather than differential drag have come to be of some interest as a means for employing wind energy to do work. Such vertical windmills are quite efficient and are able to derive power from the wind regardless of the wind direction. In theory, the upper limit of performance of differential drag windmills, or panemones, is 13 percent of the available kinetic energy in the wind. The theoretical upper limit for blade type windmills deriving performance from aerodynamic lift is 59.3 percent. Thus, the aerodynamic lift type windmills are far more efficient.
With the less efficient differential drag type windmills mounted about vertical axes, fixed baffles have been employed. These baffles are able to enhance somewhat the low performance of such windmills. In operation, the baffles act merely as wind blocking mechanisms or louvers to further reduce the drag on the low drag side of the windmill. Furthermore, the baffles are unidirectional and require that they be rotatably mounted with a trailing vane mechanism for positioning relative to the wind direction.
In spite of the advantages in efficiency of the lift type windmill over the differential drag type windmill, certain disadvantages also exist. For one, substantial blade speed is required before power may be derived from the wind. One such comparatively efficient aerodynamic lift type, vertical axis windmill must be rotated to a ratio of blade speed to wind speed of about 2.5 before net production of power can be maintained. Furthermore, the efficiency of such windmills has only been around 35 percent in spite of the theoretical maximum of 59.3 percent. Thus, both the differential drag mechanisms and the aerodynamic lift mechanisms heretofor employed have had operational disadvantages which have inhibited their use in many applications.
In employing such vertical axis windmills for other than straight mechanical work, such as pumping, it has been common to use the rotational energy developed by first generating electricity. The generated electrical power may then be used for a variety of purposes. A particularly desirable application in cold climates is to provide heat for homes and shelters. While it is possible to operate electrical heaters from electrical energy provided by windmills, the process is extremely inefficient, primarily because of the losses during energy conversion. However, the generation of electrical power makes it relatively easy to control the speed of rotation of the windmill as well as the power load on the windmill. Thus, the advantages of such a power conversion system are to be weighed against the disadvantages of mechanism complexity and loss of efficiency.